From b54cdf9f38b1476de2d519c25eb84b7bedebd613 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Tue, 23 Sep 2025 18:15:48 -0700
Subject: [PATCH] all: use buildfeatures.HasCapture const in a handful of
 places

Help out the linker's dead code elimination.

Updates #12614

Change-Id: I6c13cb44d3250bf1e3a01ad393c637da4613affb
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
---
 ipn/ipnlocal/local.go           | 6 ++++++
 net/tstun/wrap.go               | 4 ++++
 wgengine/magicsock/magicsock.go | 3 +++
 wgengine/userspace.go           | 4 ++++
 wgengine/watchdog.go            | 4 ++++
 5 files changed, 21 insertions(+)

diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 623a0a3a3..5c5fb034b 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -1026,6 +1026,9 @@ func (b *LocalBackend) onHealthChange(change health.Change) {
 // GetOrSetCaptureSink returns the current packet capture sink, creating it
 // with the provided newSink function if it does not already exist.
 func (b *LocalBackend) GetOrSetCaptureSink(newSink func() packet.CaptureSink) packet.CaptureSink {
+	if !buildfeatures.HasCapture {
+		return nil
+	}
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
@@ -1039,6 +1042,9 @@ func (b *LocalBackend) GetOrSetCaptureSink(newSink func() packet.CaptureSink) pa
 }
 
 func (b *LocalBackend) ClearCaptureSink() {
+	if !buildfeatures.HasCapture {
+		return
+	}
 	// Shut down & uninstall the sink if there are no longer
 	// any outputs on it.
 	b.mu.Lock()
diff --git a/net/tstun/wrap.go b/net/tstun/wrap.go
index 442184065..4c88c7eef 100644
--- a/net/tstun/wrap.go
+++ b/net/tstun/wrap.go
@@ -24,6 +24,7 @@ import (
 	"go4.org/mem"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"tailscale.com/disco"
+	"tailscale.com/feature/buildfeatures"
 	tsmetrics "tailscale.com/metrics"
 	"tailscale.com/net/connstats"
 	"tailscale.com/net/packet"
@@ -1491,5 +1492,8 @@ var (
 )
 
 func (t *Wrapper) InstallCaptureHook(cb packet.CaptureCallback) {
+	if !buildfeatures.HasCapture {
+		return
+	}
 	t.captureHook.Store(cb)
 }
diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index 72fff3411..0d8a1e53a 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -890,6 +890,9 @@ func deregisterMetrics(m *metrics) {
 // can be called with a nil argument to uninstall the capture
 // hook.
 func (c *Conn) InstallCaptureHook(cb packet.CaptureCallback) {
+	if !buildfeatures.HasCapture {
+		return
+	}
 	c.captureHook.Store(cb)
 }
 
diff --git a/wgengine/userspace.go b/wgengine/userspace.go
index 86136d977..7fb580514 100644
--- a/wgengine/userspace.go
+++ b/wgengine/userspace.go
@@ -23,6 +23,7 @@ import (
 	"tailscale.com/control/controlknobs"
 	"tailscale.com/drive"
 	"tailscale.com/envknob"
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/health"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/net/dns"
@@ -1652,6 +1653,9 @@ var (
 )
 
 func (e *userspaceEngine) InstallCaptureHook(cb packet.CaptureCallback) {
+	if !buildfeatures.HasCapture {
+		return
+	}
 	e.tundev.InstallCaptureHook(cb)
 	e.magicConn.InstallCaptureHook(cb)
 }
diff --git a/wgengine/watchdog.go b/wgengine/watchdog.go
index 74a191748..13bc48fb0 100644
--- a/wgengine/watchdog.go
+++ b/wgengine/watchdog.go
@@ -15,6 +15,7 @@ import (
 	"time"
 
 	"tailscale.com/envknob"
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/net/dns"
 	"tailscale.com/net/packet"
@@ -163,6 +164,9 @@ func (e *watchdogEngine) Done() <-chan struct{} {
 }
 
 func (e *watchdogEngine) InstallCaptureHook(cb packet.CaptureCallback) {
+	if !buildfeatures.HasCapture {
+		return
+	}
 	e.wrap.InstallCaptureHook(cb)
 }